This invention relates generally as indicated to a free piston engine pump, which is effective in smoothing out the energy or work rate of a free piston engine to facilitate pumping of hydraulic fluid.
A free piston engine pump differs from the usual piston engine driven pump in that the reciprocating movement of the piston is not first transmitted to a crankshaft to convert linear movement to rotary movement and then back to linear movement by means of a pump swashplate to drive the pump piston. Instead, a direct linear drive connection is provided between the engine piston and pump piston for effecting linear movement thereof. Eliminating the linear-to-rotary crankshaft elements and rotary-to-linear pump swashplate results in a substantial reduction in size and weight of the pump and also greatly improves the efficiency thereof.
Heretofore, a principal drawback in driving a free piston engine pump with an internal combustion engine is that the energy output of an internal combustion piston is very uneven over its stroke and may vary, for example, by as much as 30 to 1 during the power cycle. The maximum pressure of the Diesel cycle, for example, might typically be 1,000 psi, and the minimum pressure 30 psi, with an average pressure or MEP during the power stroke of 150 psi. The Otto cycle is similar.
A conventional engine uses a flywheel to smooth out the energy output, which in theory could also be utilized in the same way with a free piston engine. However, using a heavy mass integral or attached to the engine/pump piston to store energy during the first, accelerating portion of the power stroke, when the hydraulic work rate is much less than the engine cycle work rate, and removing such energy from the mass during the latter portion of the power stroke when the piston is decelerating is an undesirable solution for even moderate engine power because the piston mass required is much greater than that required by normal design. Also, very high velocities are required, implying large hydraulic losses, etc. Similar but less severe implications and problems would also apply to a hydraulic-powered return stroke of a free-piston engine pump, as well as to a motor-pump where gas-expansion occurs in the power cycle.